This invention relates to the identification of antimicrobial agents and of microbial targets of such agents, and in particular to the isolation of bacteriophage DNA sequences, and their translated protein products, showing anti-microbial activity. The DNA sequences can be expressed in expression vectors. These expression constructs and the proteins produced therefrom can be used for a variety of purposes including therapeutic methods and identification of microbial targets.
The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present invention.
The frequency and spectrum of antibiotic-resistant infections have, in recent years, increased in both the hospital and community. Certain infections have become essentially untreatable and are growing to epidemic proportions in the developing world as well as in institutional settings in the developed world. The staggering spread of antibiotic resistance in pathogenic bacteria has been attributed to microbial genetic characteristics, widespread use of antibiotic drugs and changes in society that enhance the transmission of drug-resistant organisms (for a review, see Cohen, 1992). This spread of drug resistant microbes is leading to ever-increasing morbidity, mortality and health-care costs.
There are over 160 antibiotics currently available for treatment of microbial infections, all based on a few basic chemical structures and targeting a small number of metabolic pathways: bacterial cell wall synthesis, protein synthesis, and DNA replication. Despite all these antibiotics, a person could succumb to an infection as a result of a resistant bacterial infection. Resistance now reaches all classes of antibiotics currently in use, including: β-lactams, fluoroquinolones, aminoglycosides, macrolide peptides, chloramphenicol, tetracyclines, rifampicin, folate inhibitors, glycopeptides, and mupirocin. There is thus a need for new antibiotics, and this need will not subside given the ability bacteria have to overcome each new agent synthesized. It is also likely that targeting new pathways will play an important role in discovery of these new antibiotics. In fact, a number of crucial cellular pathways, such as secretion, cell division, and many metabolic functions, remain untargeted today.
Most major pharmaceutical companies have on-going drug discovery programs for novel anti-microbials. These are based on screens for small molecule inhibitors (e.g., natural products, bacterial culture media, libraries of small molecules, combinatorial chemistry) of crucial metabolic pathways of the micro-organism of interest. The screening process is largely for cytotoxic compounds and in most cases is not based on a known mechanism of action of the compounds. Classical drug screening programs are being exhausted and many of these pharmaceutical companies are looking towards rational drug design programs. Several small to mid-size biotechnology companies, as well as large pharmaceutical companies, have developed systematic high-throughput sequencing programs to decipher the genetic code of specific micro-organisms of interest. The goal is to identify, through sequencing, unique biochemical pathways or intermediates that are unique to the microorganism. Knowledge of the function of these bacterial genes, may form the rationale for a drug discovery program based on the mechanism of action of the identified enzymes/proteins. However, one of the most critical steps in this approach is the ascertainment that the identified proteins and biochemical pathways are 1) non-redundant and essential for bacterial survival, and 2) constitute suitable and accessible targets for drug discovery. These two issues are not easily addressed since to date, 18 prokaryotic genomes have been sequenced and 200 sequenced genomes are expected by the year 2000. For a majority of the sequenced genomes, less than 50% of the open reading frames (ORFs) have been linked to a known function. Even with the genome of Escherichia coli (E. coli), the most extensively studied bacterium, less than two-thirds of the annotated protein coding genes showed significant similarity to genes with ascribed functions (Rusterholtz and Pohlschroder, 1999). Thus considerable work must be undertaken to identify appropriate bacterial targets for drug screening.